1. Field of the Invention
The technical field is related to an electrode unit for carrying current or voltage between an implantable electromedical device and a treatment and/or diagnosis site in the human body, wherein the electrode unit comprises at least one current-/voltage-carrying feed line and at least one electric contact pole to the body part.
2. Description of the Related Art
With respect to the background of the invention, it is noted that the subject matter of embodiments of the invention is primarily relevant in connection with cardiac pacemakers, implantable defibrillators, and other types of active implantable electromedical devices. The latter generally comprise at least one current-/voltage-carrying feed line in the electrode unit—typically referred to in short as the “electrode—, the distal end of which is disposed in a ventricle, for example, and used to measure cardiological potential signals or deliver appropriate therapeutic current signals.
The compatibility of such electrode units in implantable electromedical devices with radio frequency magnetic fields, as they are used in particular in imaging diagnostic methods based on magnetic resonance—referred to as MRI (magnetic resonance imaging) methods—represents a serious problem. Using such MRI methods, a strong static magnetic field is superimposed with an alternating magnetic field pulsed with radio frequency (RF), which is used to change the energy status of the protons in the examined tissue and produce appropriate MRI signals from the tissue.
According to the laws of electromagnetic induction, this alternating magnetic field results in alternating voltages in the feed line of the electrode units of electromedical device implants in question here, the energy of these alternating voltages being converted into heat, notably at the electrically conductive contact poles of the electrode unit with the human tissue. This may lead to considerable heating, for example of the tip contact of a cardiac electrode, along with corresponding impairment and even damage of the heart tissue in contact therewith or surrounding the same.
In order to prevent this problem, it is proposed in U.S. Pat. No. 7,363,090 B2 to use filters based on resonant circuits comprising an inductor connected in parallel with a capacitor, which is associated with the corresponding feed line for the tip contact pole or a ring contact pole of a particular electrode of an implantable electromedical device. In the practical implementation of the patent holder, the filters disclosed in this known patent are designed as comparatively bulky components that stiffen the electrode unit over a certain length and therefore lead to unfavorable mechanical properties in the electrode equipped therewith. Furthermore the filter is accommodated in a closed housing, which does not provide any leadthrough for the guide wires generally used when implanting an electrode. In this respect, the application possibilities of this known electrode comprising a filter device are limited.